1. Field of the Invention
The present invention relates to an optical packet switch device which realizes packet switching in the unit of optical packet by switching an optical switch in accordance with route information given to an optical packet signal.
2. Description of the Related Art
In an optical transmission system using wavelength division multiplexing (WDM), a technique of switching a path in the unit of wavelength has been put to practical use by using a wavelength selective switch (WSS) and so on. As the next technique, there has been considered an optical packet switching method in which the unit for switching is an IP packet (such as a 10 G Ether (10 Gigabit Ethernet™) signal), for example, each IP packet is converted into an optical packet form, and a route is switched by an ultrafast optical packet switch device. The optical packet switching method may dramatically improve the band utilization efficiency of a transmission line and thus is a promising technique for the future. In the prior art, as the optical packet switch device used in the optical packet switching method, there have been known the optical packet switch devices disclosed in patent documents No. 1 and 2, for example.    [patent document No. 1] JP 2004-354612    [patent document No. 2] JP 2008-306555
In the optical packet switch device, when the first bit of a received optical packet signal passes, an optical switch can be brought into a turned-on state, and when the last bit passes, the optical switch can be brought into a turned-off state, whereby an interval between the optical packets (hereinafter also referred to as a guard time) can be reduced, and the band utilization efficiency of a transmission line can be improved.
However, since the received optical packet signal and an operation clock in a control circuit of the optical packet switch device are asynchronous, it is actually difficult to perform the above switch control, and the optical switch is in the turned-on state for a longer time than the actual optical packet signal passing time. If the time to continue the turned-on state of the optical switch is increased, the guard time is required to be increased corresponding thereto, and therefore, the band utilization efficiency of a transmission line is reduced.
Further, in the optical packet switch device, for example when the routes of two optical packet signals input to two input ports at substantially the same timing travel toward the same output port, such a determination is performed that the first input optical packet signal is passed, and the next input optical packet signal is discarded. Such a determination is referred to as “output competition determination”. The output competition determination is usually performed by determining whether temporal overlap occurs in an electrical optical switch control signal. However, when the time when the optical switch is turned on is long as described above, even if the actual optical packet signals do not overlap temporally, the temporal overlap occurs in the optical switch control signal, and therefore, such a situation may occur that the optical packet signal is discarded. This leads to reduction in the packet loss rate and, furthermore, reduction in the band utilization efficiency of a transmission line.